This model would have the 722.4 transmission, that's a pretty bullet-proof tranny, i wouldn't give it a second thought, except to get the fluid and filter changed if the history is unknown.
Timing chain at 100K on a 104? No way in heck. Maybe in another 150K.
Look for head gasket leaks, including the front cylinder head cover (not the valve cover, although these can leak too, I mean the cover on the FRONT of the head). The signs of a leaking head gasket usually is an oil leak on the passengers side of the motor back by the rear corner. Head gasket replacement usually will set you back almost $2K if done in a shop.
Other potential for problems would be a bad wiring harness on the engine, you can do a "search" on "104 harness" here and get lots of info, although it seems most 104 harness problems occurred on 104 engines in 124 E Class cars for some odd reason. The harness replacement I would say runs in the $500-$1000 range.
If the service history is unknown, I'd plan on doing basically ALL maintenance work on the car, including coolant and brake fluid flushes and all filters. Oh, check for a leaking differential too, they like to leak on the left and right side seals and the input pinion too.

Gilly